The present invention relates to a method of electroslag remelting of metal from consumable electrode means, and particularly to electroslag remelting utilizing introduction of molten slag at the bottom of a crucible device.
In the electroslag remelting of metals, a bath of molten is obtained in a remelting zone, for example, a crucible or a mold (often referred to as a crystallizer). At least one consumable electrode is disposed to extend into that zone with its lowermost end immersed in said molten slag bath. Electric current is caused to flow from the electrode to and through the slag bath. The passage of the current through the slag bath produces heat which causes the electrode to melt. As the electrode melts, the remainder of the electrode is lowered into the slag bath so that all of the electrode is progressively melted. Because the metal in the electrode has a density greater than that of the slag bath, a molten pool of metal is formed below the slag bath. This molten pool of metal progressively solidifies into an ingot of refined metal.
Known in the prior art are methods of electroslag remelting of metal, obtained from consumable electrodes in a cooled crucible, disposed on a bottom plate; for carrying out the remelting process, a pool of molten slag is formed in said crucible.
The molten slag pool is obtained in the crucible in one case due to the melting of a solid flux or a mixture of its charge constituents during the remelting of a consumable electrode directly in the crucible. In another case, non-consumable electrodes, carbon or graphite, are employed for these purposes. This method is known as the "dry start" method.
There is also employed a flux premelted in a separate unit or a mixture of its charge constituents, followed by top pouring the molten slag thus obtained into the crucible. This method is referred to herein as "top pouring."
In the first two cases of preparing the molten slag pool, the time as required for obtaining an ingot is increased by as much as 10 to 20 percent, since the melting of slag is carried out directly in the crucible, which is likely to decrease the production rate of the plant by as much as 10 to 20 percent.
Besides, when preparing the molten slag pool with the use of consumable electrodes, there occurs an incomplete melting of the flux in the peripheral zone of the crucible which is likely to drastically impair the surface of the ingot being melted and to increase the bottom discard to be cropped during the subsequent processing of the ingot up to 10 percent.
Through the preparation of the molten slag pool in the crucible by top pouring therein the molten slag is a progressive method, which allows increasing the production rate of the plant and ensuring a high quality of the bottom part of the ingot, this method possesses its disadvantages, too.
When placing the consumable electrode in the crucible, the gap therebetween is small, and the pouring of the molten slag therein presents difficulties. The molten slag gets on the crucible walls and consumable electrode, and is likely to produce slag sows or lumps thereon. The falling off of the slag sows into the slag pool during the melting process may result in marked variations of electrical conditions of the melting process.
To eliminate said disadvantages requires that during the pouring of the molten slag the consumable electrode should be outside the crucible, for which reason the design of the plant must provide for lifting the electrode clamped in the electrode holder over the crucible so that the latter could be displaced from under the electrode for pouring the slag therein.
The short electric circuit is elongated thereby, and consequently, the losses of active energy increase therein, too, which results in a reduction of the power factor of the plant (cosl). After top pouring the molten slag into the crucible, a voltage is applied to the installation, and the consumable electrode is lowered at a maximum speed into the crucible until it is brought into contact with the slag. During this time, a crust or lining of the solid slag may form on the crucible walls and on the cooled bottom plate or a dummy bar, if it is to be placed on the bottom plate, which crust is likely to insulate the molten slag pool from the bottom plate and crucible, which results in a breaking occurring in the current circuit, and the melting process may not start.
Disadvantages of the existing plants employed for effecting the electroslag remelting of metal according to said method, consist in their excessive height, which is connected with a necessity of pouring the molten slag with the consumable electrode being raised, and with considerable losses of time as required for effecting auxiliary operations. Besides, there are required dummy bars or sacrificial plates for protecting the bottom plate against the burning through.